I would endorse the .50 caliber over the .45 caliber. There is nothing the .45 caliber can do that the .50 caliber can not match, even do better. The selection of projectiles for the .50 caliber is much better although the .45 caliber has improved. Also there are usually some excellent end of season sales on the .50 caliber. The .50 caliber has more downrange knock down. Also, why go to a smaller projectile when you want to administer as much energy into the animal as you can. Hit them as big as you can.
As for you choice of rifle, well good luck with it and be sure and stay within the safe guidelines of the manufacturer .. what ever they might be. I have a CVA and it shoots fine. Some of the recent events where they CVA/BPI barrels have failed are starting to bother me and for that reason, and the the reason that CVA does not try to explain these circumstances is why I will not endorse them anymore.
I think I would go with the NEF Sidekick in .50 caliber.
http://www.dallastacticalsupplies.com/itemdetails.asp?itemid=NESPS050instead of the Optima Pro or any other CVA for that matter. Again, I do not own a NEF and only base this on some of the post I have read about how the Sidekick performs. Good luck with your choice and selection.